Field of the Invention
The present invention relates to an image forming apparatus capable of executing calibration for maintaining color stability, and a test chart for calibration.
Description of the Related Art
In order to maintain color stability in an image forming apparatus, it is necessary to scan a measurement image (test pattern) and adjust various image processing conditions, image forming conditions, and the like. This adjustment process is referred to as “calibration”. The test pattern is scanned by a color separation type color sensor, and the appropriate exposure time differs for each color. If there is a large amount of incident light coming from the measurement subject, the exposure time needs to be shortened, and if there is a small amount of incident light, the exposure time needs to be lengthened. Japanese Patent Laid-Open No. 2007-274438 proposes a technique in which the accumulation time of light receiving elements in the color sensor is changed according to the color and density of the formed image pattern. Accordingly, it is possible to detect the color and density of the image pattern with sufficient accuracy for any color and density of an image pattern.
The sheet (test chart) on which the test patterns have been recorded is conveyed at a fixed speed. Accordingly, the length in the conveyance direction of a pattern having a long accumulation time may be longer, and the length in the conveyance direction of a pattern having a short accumulation time may be shorter. However, the length in the conveyance direction of every test pattern is conventionally a fixed length that is determined using the test pattern with the longest accumulation time as a reference. Additionally, many types of patterns are needed in order to perform calibration with a high degree of accuracy. Accordingly, the number of sheets that are needed tends to increase. Also, regarding patterns having a short accumulation time, toner has been consumed excessively in order to form patterns due to their superfluous size.